1. Field of the Invention
The present invention relates to an optical signal converter for converting an optical signal into an electrical signal, and more particularly, to an optical signal converter and a method of controlling an amplification gain according to a rotating speed of an optical disc reproducing apparatus or an optical disc reproducing and recording apparatus.
2. Description of the Related Art
FIG. 1 shows a conventional optical signal converter. Referring to FIG. 1, a conventional optical signal converter 101 includes an optical signal detector 111, a signal amplifier 121, and a gain switcher 131.
The optical signal detector 111 detects an optical signal reflected from an optical disc in a reproduction mode and converts the detected optical signal into an electrical signal.
The signal amplifier 121 amplifies a signal output from the optical signal detector 111. In this case, a rate of amplifying an optical signal is differently applied by an output of the gain switcher 131 that controls an amplification gain of the optical signal converter 101 according to a rotating speed of an optical disc. Here, the rotating speed of the optical disc is different according to types of optical discs.
Likewise, the conventional optical signal converter 101 uses a method of changing a reproduction mode into a gain mode according to types of optical discs. A speed at which data is recorded on an optical disc is gradually increased. Also, an optical power should be increased so that a data recording speed is increased.
However, even though the optical power is increased so as to record data on the optical disc at a high rotating speed, since an amplification gain of the optical signal converter 101 is fixed, an output of the conventional optical signal converter 101 is saturated.
FIGS. 2A and 2B are waveform diagrams showing input and output signals of the conventional optical signal converter 101. As shown in FIG. 2A, when the optical power is increased so as to drive the optical disc at a high rotating speed and a signal V1 reflected from the optical disc and input into the optical signal converter 101 exceeds a maximum output voltage Vmax of the optical signal converter 101, since the amplification gain of the optical signal converter 101 is fixed, an output signal Vout of the conventional optical signal converter 101 is saturated at a value Va (211) as shown in FIG. 2B, and an optical device having the optical signal converter 101 malfunctions.